A Subscriber Identity Module (“SIM”) is part of a removable smart card integrated circuit card, also known as a SIM card, for mobile cellular communication devices such as mobile phones and wireless-enabled mobile computers. The SIM card stores a variety of identification information accessed by the mobile device and/or communications network when the mobile device connects to the communications network. For instance, SIM cards securely store the International Mobile Subscriber Identity (IMSI), which is a service-subscriber key used to identify a subscriber. SIM cards also store network specific information used to authenticate and identify subscribers on the network, including the Integrated Circuit Card ID (“ICCID”), which is a serial number of the SIM card defined by the ITU-T recommendation E.118. The ICCID number is up to 18 digits long.
Other network-specific information that may be stored on a SIM card includes the International Mobile Subscriber Identifier (“IMSI”), which is a unique number associated with all GSM and Universal Mobile Telecommunications System (UMTS) network mobile phone users. The IMSI is sent by the phone to the network. It is also used to acquire other details of the mobile in the Home Location Register (HLR) or as locally copied in the Visitor Location Register. The IMSI is used in any mobile network that interconnects with other networks, in particular CDMA and EVDO networks as well as GSM nets. The IMSI is usually 15 digits long, but can be shorter, and includes the mobile subscriber identification number (MSIN) within the network's customer base.
Another important network-specific piece of information stored on the SIM card is the authentication key (“Ki”). The Ki is a 128-bit value used in authenticating the SIMs on the mobile network. Each SIM holds a unique Ki assigned to it by the operator during the personalization process. The Ki is also stored on a database (known as Authentication Center or AuC) on the carrier's network. The SIM card is not designed to allow the Ki to be obtained using the smart-card interface. Instead, the SIM card provides a function that allows the phone to pass data to the SIM card to be signed with the Ki. This, by design, makes usage of the SIM card mandatory unless the Ki can be extracted from the SIM card, or the carrier is willing to reveal the Ki.
Another important network-specific piece of information stored on the SIM card is the Location Area Identity (LAI), which provides network identification information. Operator networks are divided into Location Areas, each having a unique LAI number. When the device changes locations, it stores the new LAI in the SIM and sends it back to the operator network with its new location. If the mobile device is power cycled, the mobile device will read the previous LAI from the SIM and search for that LAI, thereby saving time in connecting to the network if the LAI has not changed.
The SIM also stores the Operator-Specific Emergency Number and carrier specific data such as the SMSC (Short Message Service Center) number, Service Provider Name (SPN), Service Dialing Numbers (SDN), Advice-Of-Charge parameters and Value Added Service (VAS) applications.